Method for extending an electrical conductor over an edge of an HDI substrate

Abstract

A process and configuration are described which enable the I/O metal fingers of any high density interconnect (HDI) module to be extended over the edge of a substrate at the end of circuit fabrication, thus enabling fabrication of circuits for arrangement in three-dimensional stacks. The module includes a first dielectric layer covering one or more electrical conductors on a substrate. The first dielectric layer is ablated to expose a portion of at least one electrical conductor and a second dielectric layer is then applied over the first dielectric layer and the exposed portion of the electrical conductor except for an extremity of the conductor. A second electrical conductor is subsequently applied and patterned to cover a portion of the second dielectric layer, the extremity of the conductor, and at least a portion of one edge of the substrate.

What is claimed is: 
     
       1. A method for extending an electrical conductor over an edge of a substrate, the conductor being situated within a first dielectric layer previously fabricated on a surface of the substrate and being conductively coupled to an integrated circuit situated on one portion of the substrate surface, comprising the steps of: ablating a part of the existing first dielectric layer on a second portion of the substrate, devoid of any integrated circuit, to expose a portion of the electrical conductor situated in the second substrate portion;   applying a second dielectric layer over at least a part of the first dielectric layer and over the second substrate portion and including the exposed electrical conductor portion, with the second dielectric layer not being applied to a region extending from an edge of the substrate onto an adjacent electrical conductor extremity portion, said edge disposed at an angle to the substrate surface; and   applying an electric-conducting extension means patterned to cover a portion of the second dielectric layer, a part of the electrical conductor extremity portion, and at least a portion of the angularly-disposed substrate edge.   
     
     
       2. The method of claim 1, wherein the second dielectric layer is applied by the SPI/epoxy-Kapton polyimide multi-lamination process. 
     
     
       3. The method of claim 1, further including the step of tapering the substrate edge. 
     
     
       4. The method of claim 1, further including the steps of: removing the electrical-conducting extension means in order to allow for rework; and reapplying a desired electrical-conducting extension means patterned to cover, after rework, a portion of the second dielectric layer, the electrically-conducting extremity, and at least a portion of the substrate edge. 
     
     
       5. A method for extending an electrical conductor over an edge of a substrate, the conductor being situated within a first dielectric layer previously fabricated on a surface of the substrate and being conductively coupled to an integrated circuit situated on one portion of the substrate surface, comprising the steps of: ablating a part of the existing first dielectric layer on a second portion of the substrate, devoid of any integrated circuit and adjacent to the substrate edge, to expose an extremity portion of the electrical conductor adjacent to an edge of the substrate, said edge disposed at an angle to the substrate surface; and   applying an electric-conducting extension means patterned to cover a portion of the first dielectric layer, a part of the electrical conductor extremity portion, and at least a portion of the angularly-disposed substrate edge.   
     
     
       6. The method of claim 5, wherein the step of ablating is performed so as to taper part of the first dielectric layer between an outermost surface of the fist dielectric layer and the substrate. 
     
     
       7. The method of claim 5, further including the steps of: removing the electrically-conducting extension means in order to allow for rework; and reapplying a desired electrical-conducting extension means patterned to cover, after rework, a portion of the first dielectric layer, the electrically-conducting extremity, and at least a portion of the substrate edge. 
     
     
       8. The method of claim 5, further including the step of tapering the edge of the substrate. 
     
     
       9. A method for extending an electrical conductor over an edge of an HDI ceramic substrate, the conductor being situated within a first dielectric layer previously fabricated on a surface of the substrate and being conductively coupled to an HDI circuit situated on one portion of the substrate surface, comprising the steps of: ablating a part of the existing first dielectric layer on a second portion of the substrate, devoid of any integrated circuit, to expose a portion of the electrical conductor situated in the second substrate portion;   applying a second dielectric layer over at least a part of the first dielectric layer and over the second substrate portion and including the exposed electrical conductor portion, with the second dielectric layer not being applied to a region extending from an edge of the substrate onto an adjacent electrical conductor extremity portion; and   applying and electric-conducting extension means patterned to cover a portion of the second dielectric layer, a part of the electrical conductor extremity portion, and at least a portion of the substrate edge disposed at an angle to the substrate surface.   
     
     
       10. The method of claim 9, wherein the second dielectric layer is applied by the SPI/epoxy-Kapton polyimide multi-lamination process.